A number of recent advances in the design of prosthetic heart valves have led to significant improvements in their function over the past several years. One such approach, that of the use of ultrathin fabric meshes to cover all nonmoving parts of a rigid valve thereby encouraging tissue ingrowth with resultant decrease in the incidence of thromboembolism complications ensued from work carried out in the principal investigator's laboratory. Other approaches include the use of a central flow disc valve and gluteraldehyde preserved tissue valves mounted on fabric covered stents. However, the efforts of most investigators working in the field of prosthetic heart valves has been directed toward the adult patient. Because of special requirements in a pediatric population and which relate to the small size of the cardiac chambers together with the growth factor, the ideal valve substitute for infants and children is not yet available. It is the research objective of this proposal to better define these requirements by anatomic and hemodynamic assessments in a pediatric population and to attempt to develop and evaluate a valve substitute better suited for use in children.